On April 20, 2010, a bubble of methane raced up the drill column of the Deepwater Horizon oil rig, bursting through the seals and barriers in its way. By the time it exploded on the platform’s surface, it had grown to 164 times its original size. The rig, severed by the explosion, caught fire and sank two days later, allowing oil and gas to spew into the Gulf of Mexico for 83 long days.

This chaotic methane bubble was just a vanguard. With the well unsealed, substantial amounts of the gas were released into the gulf. This plume of dissolved methane should have lurked in the water for years, hanging around like a massive planetary fart. But by August, it had disappeared. On three separate trips through the gulf, John Kessler from Texas A&M University couldn’t find any traces of the gas above background levels. He thinks he knows why – the methane was eaten by bacteria.

The gas pouring out of the broken well spurred the growth of bacteria called methanotrophs, which can break down methane as their only source of energy. They made short work of the gas. By the time that Kessler reached the gulf, just four months after the initial blowout, he found plenty of bacteria and precious little methane.

Kessler’s discovery goes beyond last year’s disaster. It also tells us about what happens to methane bubbles that naturally rise from the deep ocean, all over the world. Within the ocean floor, methane lies trapped within cages of ice called methane clathrates (or methane hydrates). Methane naturally escapes from these deposits, as well as from undersea vents and natural oil or gas seeps. If the gas reaches the atmosphere, it could have serious effects on the planet’s climate. After all, methane is a potent greenhouse gas and undersea clathrates contain about twice as much carbon as all the fossil fuels in the world.

But first, the gas has to reach the atmosphere, and Kessler thinks that this is unlikely. While scientists can hardly release large bursts of methane to see what happens, they can rely on “natural experiments” like the unplanned surge that followed the Deepwater Horizon well. If that gas failed to make it past the gauntlet of underwater bacteria, then natural seeps would probably meet the same fate.

Some scientists have suggested that methane freed from clathrates could have contributed to the climate upheavals behind some of Earth’s greatest extinctions events, including the day when life nearly died – the Permian-Triassic extinction. *

Greg Retallack from the University of Oregon initially backed this idea, but his mind has since changed. “I love this paper as it signals the final break with my long love affair with methane clathrate release as a cause of [the Permian-Triassic] mass extinction,” he says. “It seems that marine methane cannot even make it out of the ocean because it’s rapidly consumed there.” **

Richard Camilli, who has studied the Deepwater Horizon oil plume, agrees. He says that Kessler’s conclusions probably apply to natural methane leakages, as well as to other oil spills too. “[It] is likely to become a classic reference,” he says.

In June, when David Valentine first described the plume of oil in the Gulf, he found that most of the methane was hanging in a layer between 800 and 1200 metres down. When Kessler arrived at the same area in late August, aboard the NOAA Ship Pisces, he found no traces of it. He did, however, find the degraded remnants of oil chemical and a suspiciously low amount of oxygen.

Many methane-eating bacteria use up oxygen to break down the gas, so Kessler reasoned that the microbes had done away with the methane. He even found the bacteria in question. In September, Kessler recovered several species of methane-eating bacteria from seven different sites. In some areas, these specialists made up a third of the local bacteria.

Back in June, the methane-eaters were nowhere to be found. Instead, Valentine and Hazen detected several other groups of bacteria that were breaking down other oil hydrocarbons, such as ethane and propane. They were first on the scene. Valentine predicted that other species would follow and mop up the methane, in “boom and bust cycles of bacterial succession”. He was right. By September, the bacteria that dominated the gulf in June had all but vanished and the methane-eaters had taken their place. Even they were no longer active – they were just the remnants of a population that had bloomed in July and August.

Hazen adds that the methane-eaters “have the ability to degrade over 300 other compounds,” and may have helped the clean-up efforts in the Gulf, beyond just breaking down the methane. He has been working on ways of turning this bacterial appetite to our advantage. In 1995, Hazen patented a process for seeding polluted groundwater with methane, to stimulate the growth of bacteria that would break down the other contaminants. Many companies around the world now use this process, enticing bacterial janitors with a methane menu.

Footnotes

* This scenario was the basis of one of the worst pieces about the Deepwater Horizon disaster – a frenzied article claiming that BP’s drilling operation “may have triggered an irreversible, cascading geological Apocalypse that will culminate with the first mass extinction of life on Earth in many millions of years.” It was ably debunked.

** It’s possible that the Permian-Triassic event might have involved methane in such large amounts that it “would have overwhelmed the methanotrophs capable of handling the small Gulf spill.” But Retallack can’t find enough methane clathrates in the ocean to account for such a large plume. He still thinks that methane was still involved in the Permian extinction but now he suspects it came from disturbed coal seams.

Comments (15)

Georg

Interesting,
hours since this post is out, no response?
In this context I remember the “greenies”
hate on the dispersant mixed to the leaking oil.
They would have preferred soiled coasts
to mourn about for years?
This dispersants helped a lot to make the oil
acessible to bacterial attac.
The methane in the oil was a minor problem!.
Georg

This may be a stupid question and maybe I missed it in the article, but what are the byproducts of bacteria that consume methane? The article says bacteria use oxygen. Are there any ill effects such as creating oxygen-dead zones? Or affecting ocean acidification?

With regards to the Permian extinction, if there was a lot of methane from destabilised clathrates being oxidised in the oceans, I wonder how quickly that would use up all the dissolved oxygen. There is geological evidence (black shales, etc.) that there wasn’t much oxygen in the Permian oceans, although I think the causes, and timing relative to the extinction, are debated. Still, perhaps the clathrates still could have had something to do with it – it’s just they mucked up the oceans rather than the atmosphere.

@Georg–the issue was whether the dispersants would do more damage to the ocean ecology on a long-term basis than oil would to the shoreline ecology. Even dispersant advocates acknowledged that using it involved a tradeoff. Some “greenies” felt that BP insisted on using huge quantities of dispersant because oil on the shoreline and the damage it did would be highly visible, whereas damage to the deep ocean would be unseen and the results perhaps not apparent for years.

Minor correction to the post–Deepwater Horizon wasn’t severed from the well until it sank. In fact, the crew tried to sever the rig’s connection to the well but were unable to do so; that’s why the fire burned for two days, because it continued to be fed from the hydrocarbons coming up the riser from the well. The fire could have been extinguished and the rig possibly kept from sinking if it were only the rig itself that was burning (although that wouldn’t have affected the spill).

When the rig sank, the riser tore loose and collapsed to the sea floor. Initially there was at least one oil leak from the riser in addition to the one at the wellhead, which they managed to close off early on.

Hello Loris,
Its time to realize that green alarmists business
is very professional today!
They need pictures where they “rescue” oil drenched birds
or the like. This business is the collection of donations!
The fate of the people making their lives out of the
coast (fishermen or tourist) is not what they think of.
Did You read about the lies on area/amount of oceanic
plastic whirls these days?
Those “activists” (Green”peace” and company) are
catastrophy hoppers, never ask them for the big dramas
of yesterday.
Georg

@Georg–Well, to an extent, maybe. But it isn’t as if the environmental situation weren’t inherently alarming, or as if the donations don’t fund some important work. The oil-drenched birds would exist and need to be rescued whether pictures are taken of them or not. And many of the “greenies” DO think about how the oil spill has affected coastal residents and are trying to help them. You’re painting with a very broad brush here.

So, my question is, are there enough bacteria to eat the oil and dispersants stuck in the water? And are the degraded compounds any better for the ocean than the raw stuff?

I mean, I never even heard about the possibility of methane pollution from this disaster, and I’m glad that it didn’t cause a new Permian Extinction, but is there any hope of getting that dispersed oil cleaned up?

@Loris – ignore @Georg – he is a troll and trying to initiate flames, and indeed paints with a very broad brush that sees the world in black and white but not shades of gray.

This article, which he apparently has overlooked, is only pertaining to the methane released from DeepWater and not the other environment crippling chemicals the incident released into the environment including but not limited to dioxins from the burn off, the oil itself and the oil dispersant.

We still don’t know what long term impact this will have on the environment, and many nurseries for many species have been decimated.

I for one have no urge to play guinea pig and try the seafood from that region without further research – and if that doesn’t come across as common sense to you @Georg but rather “green alarmism” feel free to be the first to take a swim and sample the seafood down there.

Very broad brush, there is science behind the concerns of us that want to keep a beautiful planet with diverse flora and fauna for our children’s children. I guess just hard to see the argument of another when your head is wedged up your arse and your filled with delusions of grandeur over your own infallibility.

Loris: Ignore A Green Alarmist – he is a troll and trying to initiate flames, and indeed paints with a very broad brush a world that only he sees – in black and white.

The DeepWater catastrophe is a world killing even that has just begun to cascade down the death spiral.

We are clearly doomed, I feel the mother planet quaking even now. Time to wedge all our heads up our arses, where our delusions of infallibility are stored along with an appreciation of our own grandeur.

When I first encountered this story, my hype alarm rang loud and clear. Everybody said, while the well was still spouting, that the lighter fractions would be the first to degrade, and the tars would take years or centuries. Now, surprise, surprise, the lightest fraction anybody could name is found to have degraded quickly. Knock me over with a feather. Meanwhile, no word about the tar, how much of it there really is, or where it has ended up, although Interior has insisted against sense and reason that it’s all just gone.